1. Field of the Invention
The present invention relates to a method for adjusting a printing position of a dot in dot-matrix printing. Especially, it relates to a method for simplifying an adjustment process of the printing position at the time of exchange of a printing head etc. in a printing apparatus that uses a detachable printing head.
2. Description of the Related Art
In inkjet printing apparatuses, with the increased use of multiple colors in images, there have spread many ones each of which has a form such that a plurality of printing heads are mounted on a carriage and an image is printed while that carriage is being scanned. Regarding the printing head, there are many ones that are detachable to their carriages. In this case, adjustment of the printing position is regularly conducted each time the printing head is exchanged.
Hereafter, the adjustment of the printing position will be explained briefly. In the printing apparatus and the plurality of printing heads, a certain amount of variation is inevitably included therein because of its manufacture process, relationships of positions of the plurality of printing heads when being mounted on the carriage become various.
FIGS. 1A to 1D are schematic diagrams for explaining variation in placement between the printing heads when four printing heads are mounted on the carriage in parallel. In FIG. 1A, ejection outlets 94 for ejecting an ink as droplets are arranged with a predetermined pitch in a Y-direction in each of four printing heads 90 to 93. If there are no deviations in arrangements of the respective printing heads 90 to 93 and the carriages 95 to 98 on which these respective printing heads are mounted, ejection outlet arrays of the four printing heads are placed at the same position in the Y-direction in parallel as shown in the figure.
Contrary to this case, if there occurs an installation error, for example, among the printing head 91 or the carriage 96 that carries this, the ejection outlet array of the printing head 91 will have an inclination or will be shifted to the other three ejection outlet arrays. FIG. 1B shows a case where the ejection outlet array of the printing head 91 is deviated in the Y-direction compared with the other ejection outlet arrays. Moreover, FIG. 1C shows a case where the ejection outlet array of the printing head 91 is deviated in an X-direction compared with the other ejection outlet arrays. Furthermore, FIG. 1D shows a case where the ejection outlet array of the printing head 91 is inclined compared with the other ejection outlet arrays.
If there is an error of a whichever kind in a whichever direction, in the state shown in FIGS. 1B to 1D, there occurs a result that the dots printed by the printing head 91 deviate from the dots printed by the other printing heads on a printing medium. In addition, even regarding the printing head 91 alone, there is also a case where a printing position deviation occurs between the dots printed by an outward scan and the dots printed by a return scan. Then, such printing position deviations become causes of streaks or density unevenness in an image printed on the printing medium, and impair uniformity of the image.
Therefore, in the printing apparatus whose printing head is exchangeable, it was common to detect deviation quantity of the printing position from a printed test pattern and then to adjust a timing of ejecting the ink depending on the acquired deviation quantity at the time of printing as is disclosed, for example, in Japanese Patent Laid-Open No. 2002-120360.
Digressing momentarily, the printing position deviation of the printing head has several kinds as follows: a printing position deviation among the plurality of printing heads (among ink colors); a deviation caused by the inclination of the each printing head; a printing position deviation between the outward scan and the return scan. Moreover, recently, cases where inks of many more colors consisting of fundamental four colors (CMYK) plus several additional colors are used in order to enhance color reproducibility are increasingly carried out into practice. Therefore, when detecting the printing position deviation, there arises a need for printing the test patterns different in these kinds or the ink colors and detecting the deviation quantities for the respective test patterns. However, if these test patterns are printed and the respective printing position deviations are detected not only at the time of delivery of the printing apparatus but also each time the printing head is exchanged, large quantities of inks, printing media, and time will be consumed for this detection.